Theatrical lighting clamp

ABSTRACT

A quick release clamp (10) for mounting equipment such as a lighting instrument (60) on a structural member such as a pipe (36). The clamp includes a C-shaped body (12) having a jaw portion (16), a back portion (14) and a base portion (18), the jaw and base portions extending from the back portion in spaced opposing disposition. The base portion defines an adjustment aperture (22) that is formed with an internal interrupted thread (24). An elongate tubular coarse adjustment sleeve (26) defines an internal threaded central passage (28) and an external interrupted thread (30) corresponding to the internal interrupted thread of the body. The sleeve is receivable within the adjustment aperture of the body and rotatable about a longitudinal axis of the sleeve into a first position, in which the sleeve is freely movable longitudinally within the adjustment aperture, and a second position, in which the external interrupted thread of the sleeve engages and locks within the internal interrupted thread of the body to prevent longitudinal movement of the sleeve. An elongate fine adjustment bolt (34) is coaxially and threadably received within the sleeve, and is rotatable within the sleeve to project a selected amount through the sleeve towards the jaw and back portions of the body. The base portion of the body also defines a mounting passage (38) which receives the neck (42) of a mounting spigot (40) secured therein. The mounting spigot defines an elongate T-slot (52). A T-stem (58) has a T-shaped head (62) that is slidably insertable into the T-slot of the spigot through an open first end (54) of the T-slot. The head of the T-stem is selectively secured within the T-slot of the spigot by a spring-loaded latch (66) and nut (68) carried on the stem of the T-stem. The lighting instrument is secured to the stem (64) of the T-stem, and may be rapidly connected and detached from the clamps.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to clamps for mounting equipment ontostructural members, and particularly to clamps for mounting lightinginstruments onto pipes and scaffolding.

BACKGROUND OF THE INVENTION

The entertainment, theater and convention business requires repeated setup and tear down of lighting instruments in various configurations.Lighting instruments are typically supported on horizontal pipe battens,vertical boom pipes, scaffolding or other elongate structural members.The lighting instrument includes a yolk which is bolted to a clamp. Theclamp, which is most commonly a C-clamp, is then clamped onto thestructural member by tightening an adjustment bolt provided on theclamp. Lighting instruments are usually remounted to different supportstructures between various theatrical productions to obtain thepreferred lighting of the scene. Each clamp typically remains secured toits lighting instrument, so that a light can be removed from one fixedlocation and set at a new location by releasing the clamp from onesupport structure and reafixing the clamp to a different supportstructure or to a different position along the same support structure.Conventionally, side arms, hardware structures composed of a C-clamp, atubular member and a sliding "T" that can be placed along the tubularmember, may be added between the lighting instrument and the clamp whennecessary to have the lighting instrument offset horizontally from thestructural member for proper focus. In some cases, lighting instrumentsneed to be mounted on formed tracks rather than pipes, requiring the useof alternate clamping arrangements.

When unclamping a lighting instrument from a structural member, it isnecessary to back out the adjustment bolt sufficiently to allowdisengagement from the structural member. For reinstallation of theclamp, the adjustment bolt must then be rethreaded inwardly forfastening to another structural member, which may have a differentdiameter than the prior structural member with which the clamp was usednecessitating more time for reinstallation. The backing out andrethreading of the adjustment bolt is labor intensive and timeconsuming. Often in attempts to make such adjustments and to ensure afirm grip of the clamp on the structural member, adjustment bolts may beover-torqued by a technician bending the adjustment bolt. This eitherends the useful life of the clamp or poses a potential structuralweakness. A further problem of conventional clamps is that the body ismost often formed from cast iron, which may crack after repeatedoverstressing.

An example of a conventional C-clamp used for mounting lightinginstrument is disclosed in U.S. Pat. No. 1,754,929 to Atticks. This typeof clamp is commercially available from Altman Corporation. Conventionalclamps include an aperture formed in the base of the clamp into which aspigot is inserted for mounting the lighting instrument to the clamp.The spigot has an enlarged diameter head that will not pass through theaperture and a stem projecting from the aperture. The spigot isantirotatably secured within the aperture by tightening a radial setbolt carried in the base of the clamp against the stem of the spigot.The yolk of the lighting instrument is bolted to the projecting end ofthe spigot by threading a bolt into the end of the spigot. To change thelighting instrument to another mounting means, it is necessary to backout the bolt and attach another mounting means to the yoke by this samebolt. Again, this adjustment is time consuming and labor intensive.

One conventional attempt to provide a clamp that may be more rapidlyclamped and unclamped on structural members is disclosed in U.S. Pat.No. 3,784,140 to Auerbach. This clamp is sold commercially under thetrademark SURECLAMP™. The clamp includes a pivoting clamping jaw whichis actuated by turning a threaded knurl knob to loosen a lockingmechanism, which enables the rod to be moved longitudinally to pivot theclamp open and closed. While this clamp does provide for quickeradjustment, design factors of the SURECLAMP limit its use tolight-weight fixtures and the fixture position is limited to beingdirectly beneath the horizontal structural support.

An additional limitation of conventional clamps is the lack of aprovision to attach a lift line to the clamp to pull the lightinginstrument to a distant location which may be at a high elevation.Conventionally this is done by tying a line to the instrument or clamp,which is again time consuming. Additionally, once the clamp is securedin place by tightening the adjustment bolt against the structuralsupport it is sometimes desirable to secure a safety cable between thepipe and instrument. Conventionally this is done by threading the safetycable through the yolk of the instrument and around the pipe orstructural support, followed by tying or clipping the safety cable.Again, affixing safety cable is time consuming.

SUMMARY OF THE INVENTION

The present invention provides a quick release clamp for mountingequipment on a structural member. The clamp includes a C-shaped bodyhaving a jaw portion, a back portion, and a base portion. The jaw andbase portions extend from the back portion in spaced opposingdisposition. The base portion defines an adjustment aperture formed withan internal engagement surface. An elongate tubular sleeve is includedand defines an internal threaded passage and an external engagementsurface corresponding to the internal engagement surface of the body. Ina preferred embodiment of the invention, the internal engagement surfaceof the adjustment aperture of the body and the external engagementsurface of the tubular sleeve are provided with correspondinginterrupted threads. The sleeve is receivable within the adjustmentaperture of the body and is rotatable about a longitudinal axis of thesleeve between a first position, in which the sleeve is freely movablelongitudinally within the adjustment aperture, and a second position, inwhich the external engagement surface of the sleeve engages and locksagainst the internal engagement surface of the body to preventlongitudinal movement of the sleeve. In the preferred embodiment, theinterrupted threads of the body and sleeve do not engage when in thefirst position, but engage and interlock when in the second position.The clamp further includes an elongate bolt that is coaxially threadedwithin the sleeve and is rotatably advanceable within the sleeve toextend a selected amount through the sleeve towards the jaw and backportions of the body of the clamp. The body includes a mount forsecuring the body to the equipment that is to be clamped on thestructural member.

The bolt assembly formed from the sleeve and bolt provides for quickadjustment of the clamp. When the clamp is to be installed, the sleeveis slid forwardly to approximately the desired location, with the end ofthe bolt abutting the pipe or other structural member. The sleeve isthen turned to lock it into this selected longitudinal position,completing the "coarse" adjustment of the bolt. The internal bolt isthen threaded forwardly until it bears tightly against the structuralmember to complete the "fine" adjustment of the bolt to securely capturethe structural member between the body of the clamp and the bolt. Theopposite procedure is used to loosen the bolt, making for a very rapidclamping and unclamping of the clamp on the structural member. Thesurrounding of the adjustment bolt by the coaxial sleeve serves tostrengthen and reinforce the bolt to prevent bending or breakage of thebolt. This extends the life of the clamp. In addition, in the preferredembodiment the clamp is formed from a high-carbon steel rather than castiron, further strengthening and extending the life of the clamp.

In the preferred embodiment, the clamp includes a second aperturethrough which a mount is installed for attachment to the equipment to bemounted by the clamp, such as the yolk of a lighting instrument. In thepreferred embodiment, the mount comprises a spigot having an elongateneck and an enlarged diameter head. The neck is inserted through themounting aperture of the clamp from the outside of the clamp, and isretained in place by a bayonet pin inserted transversely through thedistal end of the neck. A set bolt is threaded radially through the bodyof the clamp to bear against the neck to prevent rotation of the neck.The head of the spigot includes an elongate slot having a T-shaped crosssection, an open first end and a closed second end. To mount equipmentto the spigot, a T-stem is provided which is fastened to the yoke of thelighting instrument. The T-stem includes a head that is slid into andretained within the slot of the spigot through the open first end of theslot. A nut is threaded on the exterior of the T-stem until it engagesand receives the head of the spigot to prevent withdrawal of the T-stemfrom the T-slot. The lighting instrument other equipment may be rapidlyremoved by loosening the nut and withdrawing the T-stem from the T-slot.The lighting instrument may then be reinstalled on another clamp ormounting device including a T-slot. Likewise, a different lightinginstrument or other equipment including a T-stem can be quicklyinstalled on the clamp. The spigot and set bolt of the clamp need not bereadjusted or removed for these changes.

The present invention thus provides a clamp which can be rapidly andefficiently clamped and unclamped. Lighting instruments can be rapidlyattached to and detached from the clamp through the use of the T-slotand T-stem.

In a further aspect of the invention, an aperture is provided in thebody of the clamp for attachment of a carabiner or a safety cable to theclamp. Thus a safety cable may be rapidly and securely looped throughthe instrument yoke and connected to the clamp as a fail safe and acarabiner may be rapidly and safely attached for lifting of the lightinginstrument and clamp during installation.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of thisinvention will become better understood by reference to the followingdetailed description, when taken in conjunction with the accompanyingdrawings, wherein:

FIG. 1 provides an exploded isometric view of a preferred embodiment ofthe clamp of the preset invention and the yolk of an instrument to beattached to the clamp;

FIG. 2 provides an exploded perspective view of the clamp and coarseadjustment sleeve of FIG. 1 showing details of the interrupted thread;

FIG. 3 is a cross-sectional view of the interrupted threaded aperture ofthe clamp of FIG. 1, taken substantially along line 3--3 as shown inFIG. 2, and including the profile of the coarse adjustment sleeve shownin phantom in a locked position;

FIG. 4 provides a pictorial view of the clamp of the present inventionin use mounting a lighting instrument on a pipe which is shown inphantom;

FIG. 5 is an isometric view of an alternate embodiment of a T-stem andring for use with the clamp of the present invention;

FIG. 6 a cross-sectional view of the T-stem and ring of FIG. 5 assembledto the spigot of the clamp of FIG. 1, taken along the longitudinal axisof the spigot and T-stem;

FIG. 7 is a pictorial view of the clamp of FIG. 1 mounted to a pipeshown in phantom and an isometric view of a T-stem and verticalextension rod;

FIG. 8 is an isometric view of the vertical extension rod and T-stem ofFIG. 7 of the present invention shown secured within the open side of aformed track;

FIG. 9 is a pictorial view of the T-stem and vertical extension rod ofFIG. 8 shown secured within a slot provided in the closed side of theformed track; and

FIG. 10 is a pictorial view of an alternate embodiment of the clamp ofFIG. 1 in which the mounting spigot and the clamp body are integrallyformed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The preferred embodiment of a clamp 10 constructed in accordance withthe present invention is shown in FIGS. 1 through 4. Clamp 10 includes aC-shaped body 12 including a central back portion 14 and a jaw portion16 and base portion 18 that project in spaced opposing disposition fromthe ends of the back portion 14. The base portion 18 includes anadjustment end 20 in which is formed an adjustment aperture 22. As shownin FIG. 2, the interior of the adjustment aperture 22 defines aninterrupted thread 24.

The clamp 10 further includes a coarse adjustment sleeve 26 having aninternally threaded central passage 28 (FIG. 2) and an external surfacethat defines an interrupted thread 30 corresponding to the internalinterrupted thread 24 of the body 12. When the interrupted threads 24and 30 are aligned, the sleeve 26 can be inserted freely longitudinallyinto the adjustment aperture 22. The sleeve 26 can then be rotated untilthe thread 30 contact a stop set screw 32, as shall be describedsubsequently, to lock the sleeve in place and prevent furtherlongitudinal and rotational movement of the sleeve 26 relative to thebody 12.

The clamp 10 further includes an elongate externally threaded fineadjustment bolt 34 (FIG. 1) that is threadably inserted into the centralpassage 28 of the sleeve 26. The adjustment bolt 34 is longer than thesleeve 26, so that it can be positioned to project a selected distancebeyond the distal end 35 of the sleeve 26. The bolt 34 provides for thefine adjustment of a clamping force imposed on a structural member suchas the pipe 36 indicated in FIG. 4. The pipe 36 is thus clamped securelybetween the distal end 35 of the bolt 34 and the jaw portion 16 and backportion 14 of the body 12.

The base portion 18 of the body 12 also includes a mounting passage 38(FIG. 1) into which a mounting spigot 40 is inserted. The spigot 40includes a cylindrical neck 42 and a larger diameter cylindrical base44. The neck 42 is inserted through the mounting passage 38 of the baseportion 18 from the outside of the clamp. The neck 42 is closely matchedin size to the mounting passage 38, while the base 44 is sufficientlylarge that it will not enter the mounting passage 38. After insertionthrough the mounting passage 38, a bayonet pin 46 is insertedtransversely through radial passage 47 formed radially across the distaltip of the neck 42. The bayonet pin 46 is wider than the diameter ofmounting passage 38, and thus prevents the spigot 40 from being removedfrom the mounting passage 38. A set bolt 48 is threaded into a passage50 formed radially through the base portion 18 of the body 12 and istightened against the neck 42 of the spigot 40 to antirotatably securethe spigot 40 relative to the body 12.

The base 44 of the spigot 40 defines an elongate, radially orientedT-slot 52 having an open end 54 that opens onto the outer perimeter ofthe base 44 and an interior closed end 56. The interior walls of theT-slot 52 defines a "T" profile.

The clamp 10 further includes a T-stem 58 that engages with the T-slot52 for the purpose of mounting a lighting instrument, such as thelighting instrument 60 shown in FIG. 4, or other equipment to the clamp10. The T-stem 58 includes an octagonally shaped head 62 and anexternally threaded stem 64. The head 62 of the T-stem 58 is slidablyinserted into the T-slot 52 through the open end 54 of the T-slot 52. Itis retained in place by a spring loaded latch 66 mounted on the base 44of the spigot 40. To further securely retain the T-stem 58 within thespigot 40, a nut 68 is threaded onto the stem 64 of the T-stem 58. Thenut has an annular collet flange 70 that surrounds and receives aproximal end portion of the base 44 of the spigot 40. When so secured,the nut prevents removal of the T-stem 58 from the T-slot 52. The T-stem58 further includes an internally threaded central passage 72. Amounting bolt 74 is inserted through a lock washer 76 and an aperture 78formed in the yolk 80 of the lighting instrument 60 or other equipmentto be mounted, and is threaded into the central passage 72 of the T-stem58. The yolk 80 is bolted at either end to the lighting instrument 60.In this fashion the lighting instrument 60 or other equipment that issecured to the T-stem 58 may be quickly and securely connected to theclamp 10 by sliding the head 62 of the T-stem 58 into the T-slot 52 ofthe spigot 40 and then threading the nut 68, which is convenientlyprovided with wings 82 upward to receive the proximal end portion of thebase 44 of the spigot 40. Removal of the lighting instrument 60 or otherequipment likewise requires only loosening of the nut 68, release of thespring loaded latch 66 and withdrawal of the T-stem 58 from the T-slot52 of the spigot 40.

The detailed construction of each component of the assembled clamp 10will now be described in greater detail. In so doing, the terms "bottom"and "downward" are used to refer to the direction of the base portion 18of the body 12 of the clamp 10, while the terms "upper" and "upward" areused to refer to the direction of the opposing jaw portion 16 of thebody 12 of the clamp 10. However it should be understood that the clamp10 can be used in any orientation, whether it be vertical, upside down,horizontal or otherwise. Likewise, while the clamp 10 is described foruse in mounting a lighting instrument 60, it should be understood thatvarious other lighting instruments or other pieces of equipment may besuitably mounted using the clamp 10. Clamp 10 is also described andillustrated attached to a cylindrical pipe 36 (FIGS. 4 and 7), but itshould be readily apparent that the clamp 10 is also well suited forattachment to other elongate structural members, such as rectangulartubing, scaffolding and the like.

The clamp body 12 is preferably formed from steel, which may be cast,forged, machined or otherwise worked. Referring to FIG. 2, the body 12of the clamp 10 has an interior C-shaped flange 84. The flange 84 thushas a vertical center portion corresponding to the back portion 14 ofthe body and opposing end portions oriented perpendicularly to thecenter portion that correspond to the jaw portion 16 and base portion 18of the body. The flange 84 is radiused at the junctures of the endportions and the center portion. The flange 84 defines two sets oftransverse serrations 86 on the end portion (corresponding to the jawportion 16 of the body) and the center portion (corresponding to theback portion 14 of the body), which aid in gripping the pipe 36 or otherstructural member. The flange 84 is reinforced by a C-shaped strongback88, which is integrally formed with the flange 84 and wraps around theexterior of the flange. A second transverse flange 90, also integrallyformed as part of the body, wraps the exterior of the strongback 88.

An oval caribiner aperture 91 is formed transversely through thestrongback 88 in the jaw portion 16 of the body 12. The aperture 91accommodates a caribiner for lifting the clamp or a safety line orcable.

The base portion 18 of the body includes a cylindrical boss 92 thatdefines the mounting passage 38. The mounting passage 38 and boss 92 arealigned on the longitudinal axis 94 (FIG. 1) of the mounting passage 38.The longitudinal axis 94 is oriented orthogonally relative to the endportion of the flange 84 that corresponds to the base portion 18 of thebody. The base portion 18 includes a second cylindrical portion whichforms the adjustment end 20 of the base portion 18. The cylindricaladjustment end 20 includes the adjustment aperture 22, and is orientedon the longitudinal axis 96 (FIG. 1) of the adjustment aperture 22. Theadjustment end 20 and adjustment aperture 22 are angled relative to thebase portion 18 such that the longitudinal axis 96 is pointed towardsthe juncture of the jaw portion 16 and back portion 14 of the body. Thusthe adjustment sleeve 26 and adjustment bolt 34, when mounted in theadjustment aperture 22, likewise angle towards the juncture of the jawportion 16 and back portion 14 of the body on the axis 96.

Referring next to FIG. 2, the adjustment aperture 22 of the body has asubstantially square internal cross sectional profile, with each cornerof the square profile beveled off. A left handed spiral thread, suitablyformed as an Acme thread, is formed in the interior wall of theadjustment aperture 22 about the longitudinal axis 96. Because theprofile of the adjustment aperture is square rather than round, segmentsof the thread are missing at each of the comers of the adjustmentaperture 22. Thus each interior sidewall 98 of the adjustment aperture22 includes a longitudinally spaced series of left handed spiral threadsegments 100, defined by the minor axis of the internal thread.Collectively these thread segments 100 on each of the four internal sidewalls 98 of the adjustment aperture 22 define the interrupted thread 24.Thus, the thread is "interrupted," or broken, at each of the fourcorners of the adjustment aperture 22, as can also be seen in the crosssectional view of FIG. 3. The view of FIG. 3 is taken on a cross sectionoriented orthogonally relative to the longitudinal axis 96 and viewedfrom the interior towards the exterior of the clamp. The stop set screw32 is threaded through the wall of the adjustment end 20 of the baseportion 18 to project into the interior of the adjustment aperture 22between the crests of two adjacent thread segments 100, i.e., on themajor diameter of the internal interrupted thread 24, as shown in FIG.3. This stop set screw 32 serves to prevent full rotation of theadjustment sleeve 26 within the adjustment aperture 22, as shall bedescribed subsequently.

Referring to FIGS. 1 and 2, the adjustment sleeve 26 has a correspondingset of interrupted external thread segments 102 formed about itsexterior surface, which collectively define the external interruptedthread 30. Thus the adjustment sleeve 26 has a cylindrical wall 104about which the thread segments 102 project radially to define the lefthanded spiral interrupted thread 30. When viewed endwise, the threadsegments 102 provide a substantially square external profile of thesleeve 26, with each corner of the square being beveled off at the apexof the thread segments 102. The thread segments 102 thus define fourlongitudinally oriented flat sides 106 of the sleeve 26, a longitudinalcenter portion of each side being devoid of threads to form theinterruptions in the thread segments 102.

When the flat sides 106 of the sleeve 26 are aligned with the internalsidewalls 98 of the adjustment aperture 22, the sleeve may be slidablyadvanced and retracted along longitudinal axis 96 through the adjustmentaperture 22. When oriented at the desired location, the sleeve 26 istwisted to lock into position. Because technicians will assume that thesleeve 26 has conventional right handed thread, they will twist thesleeve 26 clockwise, i.e., in the right handed direction, so that thethread segments 102 of the external interrupted thread 30 of the sleeveintermesh and engage with the thread segments 100 of the internalinterrupted thread 24 of the adjustment aperture 22. This twistingrotation in a clockwise direction can be accomplished until the crest ofone of the thread segments 102 abuts the stop set screw 32 of the body12 of the clamp, at which point further clockwise rotation is limited.This locked position is illustrated in FIG. 3, with the profile of theexternal interrupted thread 30 of the sleeve 26 being shown in phantomin the locked position. Again, this locked position is achieved bytwisting the sleeve 26 clockwise (counterclockwise as viewed in FIG. 3).If a technician attempted to twist the sleeve 26 counterclockwise (asviewed in FIG. 2), in realization that it is a left handed threaded, thestop set screw 32 would prevent rotation of the sleeve 26 and engagementof the thread segments 100 and 102.

To prevent accidental withdrawal of the sleeve 26 fully from theadjustment aperture 22, a spring clip 108 is inserted into an annulargroove formed about the exterior of the distal end 35 of the sleeve 26.The spring clip 108 is larger than the adjustment aperture 22, thussafely preventing the sleeve 26 from dropping free of the clamp body 12.The opposite, proximal end 112 of the sleeve 26 is devoid of thread, andcoaxially receives an annular collar 114 that is secured in place by aset screw 116 FIG. 1). The collar 114 is preferably knurled about itsouter surface and is graspable for manual rotation of the sleeve 26.

The fine adjustment bolt 34 is threaded through the central passage 28of the sleeve 26, and is typically maintained such that it projects aselected amount past the distal end 35 of the sleeve 26. This ispossible because the adjustment bolt 34 is longer than the sleeve 26.Because the bolt 34 is surrounded and supported about the center portionof its length by the sleeve 26, it is protected from being inadvertentlybent during normal operation.

To secure a pipe 36 or other structural member within the clamp 10, thepipe is inserted within the interior of the body 12 and pushed againstthe jaw portion 16 and back portion 14. The sleeve 26 is then slidinwardly until it contacts or approaches the pipe 36, and is then lockedinto position by turning the sleeve 26 clockwise, which backs the distaltip 35 of the sleeve 26 slightly away from the pipe 36. The adjustmentbolt 34, which has a conventional right handed thread, is then threadedinwardly in a clockwise direction until it tightly bears against thepipe 36. This rotation does not serve to disengage the sleeve 26 becauserotational forces in a clockwise direction on the sleeve 26 merely serveto keep it in the locked position. Thus only a small amount ofadjustment of the bolt 34 is required to securely clamp the pipe 36. Toremove the pipe 36, all that is necessary is to relieve tension on thebolt assembly by backing the adjustment bolt 34 out a very shortdistance through counterclockwise rotation, and then rotating theadjustment sleeve 26 in the counterclockwise direction until the flatsides 106 of the sleeve 26 are aligned with the internal sidewalls 98 ofthe adjustment aperture 22. This then permits slidable retraction of theassembled sleeve 26 and bolt 34 as a unit.

If, while the pipe 36 is securely clamped by the clamp 10, someoneunintentionally were to turn the sleeve 26 clockwise, this would have noimpact because the sleeve is already in a clockwise locked position withthe interrupted external thread segments 102 against the stop screw 32.If someone inadvertently should try to turn the coarse adjustment sleeve26 in the counterclockwise position, as would be necessary to unlock theinterrupted threads, the left handed spiral of the threads would causethe sleeve 26 to attempt to move forwardly towards the pipe 36, thusmerely further tightening the clamp on the pipe 36. Thus the sleeve 26cannot be rotated counterclockwise to the unlocked position until theadjustment bolt 34 has first been manually loosened one or two turns,ensuring that the clamp is not accidentally loosened.

The use of a left handed spiral interrupted thread on the sleeve 26 isthus highly desirable for the purposes of both allowing quick and lowlabor clamping and unclamping of the clamp 10, and to prevent accidentalunclamping of the clamp 10. It should be apparent to those of ordinaryskill in the art that a right handed spiral interrupted thread wouldalso serve to suitably permit rapid clamping and unclamping of the clamp10 of the present invention. However, a right handed spiral interruptedthread, or a straight (non-spiral) square interrupted thread, which isalso feasible, are not the most preferred because of the above notedsafety advantages of the left handed spiral. It should also be apparentto those of ordinary skill in the art that other types of engagingsurfaces for the exterior of the adjustment sleeve 26 and interior ofthe adjustment aperture 22 could be adapted within the scope of thepresent invention, such as: eccentrically shaped engaging surfaces (notshown); the provision of a stop on the sleeve 26 that would engage in aselected one of a series of spiral grooves formed in the interior of theadjustment aperture 22 (not shown); or the converse formation of aseries of spiral grooves on the exterior of the adjustment sleeve thatengage with a pin carried on the interior of the adjustment aperture(not shown).

Attention is now directed to FIG. 1 for description of the quick releasemounting of the instrument 60 or other equipment to the clamp 10. Themounting spigot 40, as previously described, includes a cylindrical neck42 that is inserted through the mounting passage 38 of the body 12, andis secured in place by the transversely inserted bayonet pin 46 and setbolt 48. It should be readily apparent to those of ordinary skill in theart that a mounting spigot 40 and clamp body 12 could be integrallyformed as a one piece casting or forging 200, as shown in FIG. 10. Thebase 44 of the spigot 40 would thus be formed as an integral extensionof the boss 92 of the base portion 18. However, for purposes ofretrofitting existing clamps, which include mounting passages toaccommodate conventional spigots, the spigot 40 of the preferredembodiment of the clamp 10 illustrated is formed separately from theclamp body 12. Thus the spigot 40 could be mounted within the body of aconventional clamp to provide a clamp with a quick release of lightinginstruments and other equipment from the clamp. However, such a modifiedconventional clamp including the mounting spigot 40 of the presentinvention would not include the quick release clamping and unclampingadvantages provided by the screw 26 and bolt 34 of the presentinvention.

The neck 42 of the mounting spigot 40 includes an internally threadedcentral passage 118. This is intended to allow the threadable connectionof other structures to the distal end of the spigot 40 when removed fromthe clamp body 12, for connection to T-stems 58 of the presentinvention, thus providing further adaptability of the components of theclamp 10.

Referring still to FIG. 1, the base 44 of the spigot 40 has a generallycylindrical configuration. The base 44 and neck 42 are aligned upon acommon longitudinal axis, which is aligned with longitudinal axis 94 ofthe mounting passage 38 when the spigot 40 is assembled to the clampbody 12. The T-slot 52 is formed radially into the base 44. The T-slotextends from the open first end 54 of the T-slot to the closed secondend 56 within the interior of the base 44. Viewed in profile, the T-slot54 has a wide upper portion and a downwardly opening narrower bottomportion. The width of the top portion of the T-slot 52 corresponds tothe flat face-to-flat face diameter of the octagonal head 62 of theT-stem 58. The width of the narrow bottom portion of the T-slot 52corresponds to the width of the stem 64 of the T-stem 58.

The T-slot 52 is configured in dimension such that when the T-stem isslid into the T-slot, the head 62 of the T-stem is closely receivedwithin the wide upper portion of the T-slot 52, with opposing flat facesof the octagonal head 62 contacting the interior sidewalls of the wideupper portion of the T-slot 52. This prevents rotation of the T-stem 58within the T-slot 52. When fully inserted within the T-slot 52, the stem64 of the T-stem 58 contacts the closed second end 56 of the narrowbottom portion of the T-slot 52, and in this position is longitudinallyaligned with the mounting spigot 40 on the longitudinal axis 94. TheT-stem 58 can be inserted and removed from the T-slot 52 only throughthe open first end 54 of the T-slot 52. Once inserted, inadvertentwithdrawal is prevented by the spring loaded latch 66. The spring loadedlatch 66 is biased to project downwardly into the interior of the T-slot52, abutting against the radial and outermost flat face of the head 62when it is fully inserted into the T-slot 52. In this position, thelatch 66, which is illustrated and described in greater detailsubsequently, physically blocks the head 62 so that it can not bewithdrawn from the T-slot 52.

The proximal or bottom end of the base 44 of the spigot 40 is beveledabout its outer periphery. The nut 68 that is threaded onto the stem 64of the T-stem 58 includes an upwardly projecting collet flange 70 formedabout its outer periphery. The interior surface of the collet flange 70is correspondingly beveled to the bevel of the proximal bottom end ofthe base 44 of the spigot 40. After the T-stem 58 has been slid into theT-slot 52, the nut 68 can be threaded upwardly by pushing on the nutwings 82. As the nut 68 moves upwardly to receive the bottom proximalend of the base 44 of the spigot 40, the corresponding beveled surfacesof the base 44 and the collet flange 70 come into contact, causingautomatic centering of the T-stem 58 relative to the spigot 40. Becausethe flange 70 receives and surrounds the bottom proximal portion of thebase 44, it also acts to prevent withdrawal of the T-stem 58 from theT-slot 52. Withdrawal of the T-stem 58 can be readily affected, however,by backing the nut 68 downwardly until it no longer receives the base 44of the spigot 40, and then lifting upwardly on the latch 66 to withdrawthe latch 66 from the interior of the T-slot 52.

Attention is now directed to FIGS. 5 and 6 for description of analternate configuration of the T-stem 58. Instead of providing a onepiece T-stem 58 including a octagonal head 62, a round headed T-stem 120and locking ring 121 assembly is provided. The round headed T-stem 120is identical to the octagonal T-stem 58 previously described except forthe following differences. The head 122 of the T-stem 120 has a circularcircumference. An annular groove 124 is formed about the perimeter ofthe head 122. The annular groove 124 serves to retain the ring 121 onthe head 122 of the T-stem 120 when the head 122 is not received in theT-slot 52 of the spigot 40. The ring 121 is provided with two springwires 125, each inserted tangentially through the sidewall of the ring121. The spring wires 125 are oriented such that the wires snap withinthe groove 124 upon pushing the head 122 into the recess 130. Thisserves to retain the ring 121 while still permitting the ring 121 torotate on the T-stem 120, until compressed.

Below the groove 124, the perimeter of the head 122 is beveled. Theannular ring 121 has an internal passage 126 which receives the stem 128of the T-stem 120. The ring 121 includes an annular recess 130 definedin its upper surface that is dimensioned to correspond to the contour ofthe head 122. Thus a bottom inner wall portion 132 of the recess 130 isalso beveled corresponding to the bevel of the head 122. However, thediameter of the beveled portion 132 is slightly less than the diameterof the beveled portion of the head 122, so that when the head 122 isreceived within the recess 130 of the ring 121 the corresponding beveledsurfaces contact each other closely. Compression of the ring 121 andhead 122 together causes these beveled surfaces to bind, such that whenso compressed the T-stem 120 does not rotate relative to the ring 121.The interference fit of the beveled surfaces of the ring 121 and head120 is very slight, and typically can be provided by manufacturingtolerances.

The exterior perimeter of the ring 121 is octagonally shaped,corresponding to the octagonal shape of the head 62 of the previouslydescribed T-stem 58. The ring 121 is placed on the stem 128 of theT-stem 120 between the head 122 and the nut 68. The head 122 of theT-stem 120 is received within the upward facing recess 130 of the ring121, and the head 122 and ring 121 are slid as an assembly into theT-slot 52 of the spigot 40. When the nut 68 is threaded upwardly toreceive the bottom proximal portion of the base 44 of the spigot 40, theT-stem 120 is drawn downwardly to compress the head 122 and the ring 121together. Thus this compression antirotatably locks the ring 121 andhead 122 together, and the octagonal outer surface of the ring 121antirotatably secures this assembly against the sidewalls of the slot52.

FIG. 6 further illustrates the spring loaded latch 66. The spring loadedlatch 66 includes a dog legged latch 134 including a latch portion 136and an actuating portion 138. The latch portion 136 projects downwardlythrough the base 44 of the spigot 40 into the T-slot 52. The actuatingportion 138 projects radially outwardly from the upper end of the latchportion 136 for grasping to move the latch 134 in and out of the T-slot52. A leaf spring 140 is compressed between the actuating portion 138 ofthe latch 134 and a housing 142 which surrounds the latch 134. The leafspring 140, which could alternately be configured as a coil spring orother biasing device, serves to bias the latch 134 downwardly into thelocked position within the T-slot 52. The actuating portion 138 of thelatch 134 can be pressed upwardly to compress the spring 140 to removethe latch 134 from the T-slot 52.

It should be apparent that rather than a latch 66 as described, othertypes of safety latches could be employed. Thus, a springloaded detentball (not shown) could be mounted in the top of the T-slot 52 whichwould engage with a detent formed in the upper surface of the T-stem 58or 120. Likewise, rather than including beveled mating surfaces on thering 121 and T-stem 120 described above, other types of engagingsurfaces could be employed. For example, the bottom lip of the head 122of the T-stem 120 could be formed with a series of radial ratchet teeth(not shown) which would engage with an annular series of radial ratchetgrooves (not shown) formed in the bottom of the recess 130 of the ring121. Likewise, in place of ratchet teeth and grooves, a frictionalgasket such as a leather gasket could be mounted between the head 122 ofthe T-stem 120 and the ring 121.

FIG. 7 illustrates the clamp 10 and T-stem 58 of the present inventionadapted for use with an extension rod 144. The clamp 10 is configuredthe same as previously described, as are the T-stem 58 and nut 68. Thestem 64 of the T-stem 58 (configured as a longer bolt with an octagonalhead 62, as illustrated) is threaded into one end of a tubular extensionrod 144. A radially oriented set screw 146 is threaded in to bearagainst the stem 64 to prevent them from becoming inadvertentlyunthreaded. The nut 68 is positioned on the stem 64 between the head 62and the extension rod 144. The T-stem 58 engages with the T-slot 52 ofthe spigot 40 exactly as previously described to mount the clamp 10 onthe end of the extension rod. The opposite end of the extension rod 144can be provided with a second spigot 40, configured exactly as thepreviously described spigot 40 of the clamp 10. The bayonet pin 46 isinserted transversely through the tubular extension rod 144 to captureand secure the upper end of the neck 42 of the spigot 40. By unthreadingthe set screw 146 and removing the bayonet pin 46, the T-stem 58 and thespigot 40 may be easily removed from the extension rod 144. The T-stem58 and spigot 40 can then be placed on other tubular extension rods, orother tubular members that have a greater or shorter length than theextension rod 144.

FIGS. 8 and 9 illustrate alternate uses of an extension rod 144 providedon one end with a spigot 40 of the present invention and on the otherend with a T-stem 58 and nut 68 of the present invention, as previouslydescribed in FIG. 7. However, rather than mounting the T-stem 58 to aclamp 10 of the present invention, the T-stem is mounted to a length ofstructural track 148 (only a portion of which is illustrated).Conventional track used in theatrical lighting has a generally squaretubular outer profile. The track 148 has three longitudinal,solid-walled sides 150. The fourth longitudinal wall of the track 148includes a longitudinal slot 152. The head 62 of the T-stem 58 can beinserted endwise into the track 148 (as shown in FIG. 8), with the stem64 of the T-stem 58 being received within the slot 152 of the track 148.The nut 68 is then turned to bear against this open longitudinal side ofthe track 148 to clamp the edges of the slot 152 between the head 62 ofthe T-stem 58 and the nut 68. A conventional type of structural tracksuitable for use with the T-stem 58 of the present invention is theUnistrut™ Model 1000 track.

FIGS. 8 and 9 include a modification to conventional track. A spacedseries of elongate engagement slots 154 (only one being illustrated) isformed along the length of the track 148 in the solid longitudinal side150 opposite the longitudinal slot 152. Each engagement slot 154includes a wide end 156 which has a width corresponding to the width ofthe head 62 of the T-stem 58, and a narrow end 158, corresponding inwidth to the stem 64. As shown in FIG. 9, the extension rod 144 can bemounted to this longitudinal side 150 of the track 148, opposite of theslot 152, by inserting the head 62 of the T-stem 58 into the wide end156 of the engagement slot 154. The head is then slid longitudinallyuntil the stem 64 is received within the narrow end 158 of theengagement slot 154, and the nut 68 is tightened down to securely jointhe extension rod 144 to the track 148.

While the preferred embodiment of the invention has been illustrated anddescribed, it will be appreciated that various changes can be madetherein without departing from the spirit and scope of the invention. Itis therefor intended that the scope of letters patent granted hereon belimited only by the definitions contained in the appended claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A quick release clampfor mounting equipment on a structural member, comprising:a C-shapedbody having a jaw portion, a back portion, and a base portion, the jawand base portions extending from the back portion in opposing spaceddisposition, the base portion defining an adjustment aperture, whereinthe adjustment aperture is formed with an internal interrupted thread;an elongate tubular sleeve defining an internal uninterrupted threadedpassage and an external interrupted thread, the sleeve being receivablewithin the adjustment aperture of the body and rotatable about alongitudinal axis of the sleeve between a first position, in which thesleeve is freely movable longitudinally within the adjustment aperture,and a second position, in which the external interrupted thread of thesleeve engages and locks within the internal interrupted thread of thebody to prevent longitudinal movement of the sleeve; an elongate boltcoaxially and threadably received within the sleeve and rotatable withinthe sleeve to project a selected amount through the sleeve towards thejaw and back portions of the body to securely capture the structuralmember therebetween; and mounting means formed on the body for securingthe body to the equipment.
 2. The clamp of claim 1, wherein the externalinterrupted thread of the sleeve defines a square external profile andthe internal interrupted thread of the body defines a square internalprofile when viewed endwise along the longitudinal axis of the sleeve.3. The clamp of claim 2, wherein the internal interrupted thread of thebody and the external interrupted thread of the sleeve are spirallyformed.
 4. The clamp of claim 3, wherein the internal interrupted threadof the body and external interrupted thread of the sleeve are formedwith a left-handed spiral.
 5. The clamp of claim 4, further comprising astop formed on the major diameter of the internal interrupted thread ofthe body to limit the complete rotation of the tubular sleeve relativeto the body for locking of the sleeve within the adjustment aperturewhen the sleeve is rotated to the second position.
 6. The clamp of claim1, wherein the body further defines a carabiner/safety cable apertureformed tranversely through one of the jaw and back portions of the body.7. The clamp of claim 1, wherein the mounting means comprises a mountingpassage capable of receiving a mounting spigot that is selectivelysecurable to the equipment.
 8. The clamp of claim 7, wherein themounting means further comprises a mounting spigot including an elongateneck and a base, the neck being insertable through the mounting passageof the body, and securement means for securing the neck of the mountingspigot within the mounting passage of the body, wherein the base of themounting spigot defines an elongate slot having a T-shapedcross-sectional profile, an open first end and a closed second end. 9.The clamp of claim 8, further comprising means for preventing rotationof the spigot relative to the body.
 10. The clamp of claim 8, furthercomprising a stop that is mounted within the spigot and that is biasedto project inwardly into the slot to block the open end of the slot andthat is selectively withdrawable from the slot.
 11. The clamp of claim8, further comprising a T-stem having an elongate stem securable to theequipment and a T-shaped head slidably insertable into the slot of thespigot through only the open first end of the slot.
 12. The clamp ofclaim 11, wherein the stem of the T-stem is externally threaded, furthercomprising a nut threadably engaged on the exterior of the stem andthreadably advanceable on the stem toward the spigot when the head ofthe T-stem has been inserted into the slot of the spigot until the nutcontacts the spigot to prevent removal of the head from the slot. 13.The clamp of claim 12, wherein the nut engages the base of the mountingspigot so as to center the T-stem relative to the mounting spigot. 14.The clamp of claim 13, wherein the nut includes an annular lip thatreceives the base of the mounting spigot when the nut has been tightenedagainst the mounting spigot.
 15. The clamp of claim 11, furthercomprising means for preventing rotation of the T-stem relative to themounting spigot.
 16. The clamp of claim 15, wherein the means forpreventing rotation comprises first and second flat sides formed on thehead of the T-stem that contact corresponding internal surfaces of theslot of the mounting spigot when the head of the T-stem is inserted intothe slot.
 17. The clamp of claim 15, wherein the means for preventingrotation comprises an annular ring, the ring being receivable on thestem of the T-stem between the head of the T-stem and the nut, the headof the T-stem and the ring forming corresponding engaging surfaces suchthat when the head is compressed against the ring, the head is preventedfrom rotating relative to the ring, wherein the ring has first andsecond flat sides that contact corresponding internal surfaces of theslot of the mounting spigot when the ring is inserted with the head intothe slot of the mounting spigot.
 18. The clamp of claim 17, wherein theengaging surfaces of the ring and head of the T-stem comprise matingannular beveled surfaces.
 19. The clamp of claim 1, wherein the mountingmeans comprises a boss provided on the body and adapted to include abase defining an elongate slot having a T-shaped cross-sectionalprofile, an open first end and a closed second end.
 20. The clamp ofclaim 19, further comprising a T-stem having an elongate stem securableto the equipment and a T-shaped head slidably insertable into the slotof the base through only the open first end of the slot.
 21. The clampof claim 20, wherein the stem of the T-stem is externally threaded,further comprising a nut threadably engaged on the exterior of the stemand threadably advanceable on the stem toward the base when the head ofthe T-stem has been inserted into the slot of the base until the nutcontacts the base to prevent removal of the head from the slot.
 22. Theclamp of claim 21, wherein the nut engages the base so as to center theT-stem relative to the base.
 23. The clamp of claim 22, wherein the nutincludes an annular lip that receives the boss when the nut has beentightened against the base.
 24. The clamp of claim 19, furthercomprising means for preventing rotation of the T-stem relative to thebase.
 25. The clamp of claim 24, wherein the means for preventingrotation comprises first and second flat sides formed on the head of theT-stem that contact corresponding internal surfaces of the slot when thehead of the T-stem is inserted into the slot of the base.
 26. The clampof claim 24, wherein the means for preventing rotation comprises anannular ring, the ring being receivable on the stem of the T-stembetween the head of the T-stem and the nut, the head of the T-stem andthe ring forming corresponding engaging surfaces such that when the headis compressed against the ring, the head is prevented from rotatingrelative to the ring, wherein the ring has first and second flat sidesthat contact corresponding internal surfaces of the slot of the basewhen the ring is inserted with the head into the slot of the base. 27.The clamp of claim 26, wherein the engaging surfaces of the ring andhead of the T-stem are selected from the group consisting of matingannular beveled surfaces and mating annular ratchet surfaces.
 28. Aquick release clamp for mounting equipment on a structural member,comprising:a C-shaped body having a jaw portion, a back portion, and abase portion, the jaw and base portion extending from the back portionin spaced opposing disposition, the base portion defining in adjustmentaperture, wherein the adjustment aperture is formed with an internalengagement surface; an elongate tubular sleeve defining an internalthreaded passage and an external engagement surface, the sleeve beingreceivable within the adjustment aperture of the body and positionablebetween a first position, in which the sleeve is freely movablelongitudinally within the adjustment aperture, and a second position, inwhich the external engagement surface of the sleeve engages and locksagainst the internal engagement surface of the body to preventlongitudinal movement of the sleeve; an elongate bolt coaxially andthreadably received within the sleeve and rotatable within the sleeve toproject a selected amount through the sleeve towards the jaw and backportions of the body to securely capture the structural membertherebetween; and a mount formed on the body for securing the body tothe equipment.
 29. A clamp assembly for mounting equipment on astructural member, comprising:a C-shaped body having a jaw portion, aback portion and a base portion, the jaw and base portions extendingfrom the back portion in spaced opposing disposition, the base portiondefining an internally threaded aperture; an elongate bolt threadablyreceived within the aperture and rotatable to project a selected amounttowards the jaw and back portions of the body to securely capture thestructural member therebetween; a boss provided on the body, the bossincluding a base defining an elongate slot having a T-shapedcross-sectional profile, an open first end and a closed second end; aT-stem having an elongate stem securable to the equipment and a T-shapedhead slidably insertable into the slot of the base through only the openfirst end of the slot; and means for selectively securing the head ofthe T-stem to prevent withdrawal of the head from the slot.
 30. Theclamp assembly of claim 29, wherein the means for selectively securingcomprises a nut that is threadable onto the stem of the T-stem and thatcan be threadably advanced to receive the base when the head of theT-stem is inserted into the slot of the base.
 31. The clamp assembly ofclaim 29, wherein the means for selectively retaining further comprisesa stop mounted within the base and biased to project inwardly into theslot to prevent withdrawal of the head of the T-stem from the slot andbeing selectively withdrawable from the slot to enable withdrawal of thehead of the T-stem from the slot.
 32. A clamp assembly for mountingequipment on a structural member, comprising:a C-shaped body having ajaw portion, a back portion and a base portion, the jaw and base portionextending from the back portion in spaced opposing disposition, the baseportion defining an internally threaded aperture; an elongate boltthreadably received within the aperture and rotatable to extend aselected amount towards the jaw and back portions of the body tosecurely capture the structural member therebetween; sand a bossprovided on the body, the boss including a base defining an elongateslot having a T-shaped cross-sectional profile, an open first end and aclosed second end.